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/* crcdrm.c
* another CRC 16
* Copyright 2006, British Broadcasting Corporation
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
* Copyright 1998 Gerald Combs
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdlib.h>
#include <wsutil/crcdrm.h>
unsigned long crc_drm(const char *data, size_t bytesize,
unsigned short num_crc_bits, unsigned long crc_gen, int invert)
{
unsigned long crc_holder, ones, i, msb, databit;
signed short j;
ones = (1 << num_crc_bits) - 1;
crc_holder = ones;
for (i=0; i<bytesize; i++)
for (j=7; j>=0; j--)
{
crc_holder <<= 1;
msb = crc_holder >> num_crc_bits;
databit = (data[i] >> j) & 1;
if ((msb ^ databit) != 0)
crc_holder = crc_holder ^ crc_gen;
crc_holder = crc_holder & ones;
}
if (invert)
crc_holder = crc_holder ^ ones; /* invert checksum */
return crc_holder;
}
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